Protocols 2-4 will explore the mechanisms by which the oral mandibular advancement device prevents pharyngeal airway closure. These latter protocols are designed to validate our anatomic model explaining the effect of the oral device on the pharyngeal airway. Protocol 2 will test the hypothesis that OSA subjects with closure in the lower pharyngeal airway will have the greatest improvement with the oral device but that some patients with closure in the upper pharyngeal airway will also have a therapeutic response. Protocol 3 will test the hypothesis that the oral mandibular advancement device prevents pharyngeal airway closure by decreasing critical airway pressure. Protocol 4 will determine whether or not the ability of the oral mandibular advancement device to prevent pharyngeal airway closure is dependent on the amount of bite opening on the device. Understanding the device's mechanical effects on pharyngeal airway function will lead to improved design of oral devices and may identify physiologic parameters that predict which OSA patients will respond to this treatment. The ability to predict the polysomnographic response to treatment with the oral device and improvement in design will allow oral mandibular advancement devices to become a primary treatment alternative for many OSA patients.